1. Field of the Invention
The invention relates to a pixel structure and particularly relates to a pixel structure having high aperture ratio and favorable display quality.
2. Description of Related Art
With advantages of high definition, small size, light weight, low driving voltage, low power consumption, and an extensive range of application, a liquid crystal display (LCD) has replaced a cathode ray tube (CRT) display and becomes a mainstream among various display products. The conventional liquid crystal panel is formed by a color filter substrate, a thin-film transistor array substrate, and a liquid crystal layer disposed between the foregoing two substrates. To improve display quality, various layout designs of pixel structures for liquid crystal panels have been proposed.
FIG. 1 is a schematic top view of a conventional pixel structure. Referring to FIG. 1, a substrate 101 has an array of a plurality of pixel areas 102, and a pixel structure 100 is disposed in each of the pixel areas 102. In the drawing, only one of the pixel areas 102 is depicted for reference. The pixel structure 100 includes a scan line 110 and a gate electrode 112, a common electrode 114 and a common electrode 116, a semiconductor layer 122, a data line 130, a source 132 and a drain 134, and a pixel electrode 150. The common electrodes 114 and 116 are disposed to increase the storage capacitance in the pixel structure 100, so as to maintain the display quality.
The pixel structure 100 is a thin-film transistor pixel structure fabricated by conventional five photomask processes. The conventional five photomask processes include: a first photomask process for forming the scan line 110, the gate electrode 112, and the common electrodes 114 and 116; a second photomask process for forming the semiconductor layer 122; a third photomask process for forming the data line 130, the source 132, and the drain 134; a fourth photomask process for forming a contact window CH above the drain 134; and a fifth photomask process for forming the pixel electrode 150.
Because the scan line 110, the data line 130, the thin-film transistor (formed by the gate electrode 112, the source 132, and the drain 134), and the common electrodes 114 and 116 in the pixel structure 100 are formed by opaque metal layers, the aperture ratio of the pixel structure 100 is reduced by these opaque metal layers. Although the common electrodes 114 and 116 can increase the storage capacitance of the pixel structure 100, the aperture ratio of the pixel structure 100 is lowered as the area occupied by the common electrodes 114 and 116 in each pixel area increases.
When the pixel structure 100 is applied in a high-resolution portable liquid crystal display device, the space for each pixel area 102 is narrowed. As a consequence, the aperture ratio of the pixel structure 100 is limited to about 52%, which is lower than the aperture ratios of general televisions or monitors. To maintain the display brightness of the pixel structure 100, it is required to increase intensity of light sources in the display device, which is a waste of energy.
In addition, the common electrode 114 and the scan line 110 of the pixel structure 100 are formed on the substrate 101 at the same time. When the common electrode 114 and the scan line 110 are close to each other, short circuit may easily occur between the common electrode 114 and the scan line 110, which reduces the yield rate of the production.